The process of cooking in a conventional gas or electric oven is relatively uncomplicated. Generally, temperature and time are the only two cooking parameters considered. Normally, the oven is preheated to a given temperature and the food is placed in the oven for a specified time period which is sometimes determined by the weight of the food. For example, it may be preferable to cook a turkey at 350.degree. F. for 20 minutes per pound. Generally speaking, the heat at the surface of the food gradually travels inward by conduction raising the temperature of the interior and causing physical changes which are part of the cooking process. Because this cooking process is relatively slow and is always limited by the temperature of the oven so that there can be no thermal runaway, there is a reasonable tolerance in the selection of the cooking parameters. For example, a deviation of 10 minutes per hour or 25.degree. F. in temperature may not have a significant impact on the palatability of the cooked food. This tolerance has contributed to a general confidence of most cooks of their ability to accurately select temperature and time, even in new situations. Another contributing factor is exposure in that most cooks grew up in homes where all of the cooking was done in conventional gas or electric ovens.
The microwave oven has evolved in the last two or three decades. Although consumer acceptance has greatly increased as has the percentage of households with microwave ovens, some consumers are still reluctant to buy or use microwave ovens because they don't have the general confidence in their ability to operate them; they feel intimidated by the sometimes complicated directions for using them. They no longer have the comfortable parameters of temperature and time to select. The introduction or indoctrination into a relatively new cooking process is complicated by the rate at which foods cook. More specifically, because a microwave oven cooks so fast, an error of a few minutes in the selected cooking time can be a substantial percentage of the required cooking time and can result in a substantial difference in the doneness of the food. Furthermore, the temperature of the food body is not limited by the temperature of the oven; temperature runaway can occur. Accordingly, microwave oven manufacturers have expended considerable effort in research and development of apparatus and methods for simplifying the user task of determining the cooking parameters for microwave ovens. Simplified user operation would presumably expand the consumer marketplace.
One prior art approach was to provide a temperature probe which the user inserts in the food body. The oven is then permitted to remain on until the internal temperature rises to a selected value. This method has the disadvantage of the inconvenience of inserting the probe especially in frozen food. Also, there has been difficulty positioning the probe and the food in the oven and connecting the cable attached to the probe to a jack in the cavity. However, the most serious drawback is that the measure of internal temperature in a food body heated by microwave energy is not an indication of doneness. Actually, the food body should generally be heated up to approximately 160.degree. F. and then held there while the cooking process occurs.
Other types of approaches have used various sensors in the oven cavity to monitor the cooking characteristics of the food. None of these approaches has met with total consumer acceptance.